The long-term objective of this application is to elucidate the roles of pulmonary afferents in cardiopulmonary diseases. Hyperpnea, tachypnea and dyspnea are common symptoms and signs of cardiopulmonary patients. Those patients often hyperventilate, which is detrimental to their existing disease. There are several types of nerve endings in the lung, which provide the respiratory center with information about mechanical and chemical changes. However, what roles these nerve endings play are still not fully understood. Recently, a vagally mediated 'excitatory lung reflex' is described. Initiation of the reflex may be a key step for the hyperpnea, tachypnea as well as dyspnea during cardiopulmonary diseases. Our preliminary data indicate that the receptor endings for the reflex are located in the small airways. The specific aims of this project are to identify the structure, mechanical and chemical properties of the responsible endings and to identify their afferent pathways. Phrenic nerve activity and intraluminal pressure in the trachea will be recorded for assessing respiration. The activity in the sensory endings will be recorded to quantify the afferent response. Using neurological and pharmacological methodology to stimulate or block nerve traffic, the reflex effects will be assessed, the reflex pathway will be established and the mechanisms for activation of the receptors will be explored. These physiological results will be confirmed by morphological studies with the techniques such as, neural tracing and histochemistry. The information gained will improve our understanding of neural control of breathing, leading to better clinical management of pulmonary problems.